A map from Wikipedia showing distribution of native speakers (dark green) and other regions of use (light green):

3. Number of Speakers / Nombre de locuteurs

According to Ethnologue: 2,037,929 in Democratic Republic of the Congo (2000 WCD). Second-language speakers together with Bangala in Democratic Republic of the Congo: 7,000,000 (1999 WA). ... 90,553 in Congo (2000 WCD)... Population total all countries: 2,139,202.

4. Dialect Survey / Enquête de dialecte

No dialect survey has come to our attention as of this writing. There are many varieties of Lingala. Most materials are prepared in one of two styles, either in classical/literary Lingala or in popular Lingala. It is felt by many that the two varieties are not mutually intelligible. (Webbook)

[Lingala is] close to Lusengo and Bangala. (Ethnologue)

5. Usage / Utilisation

Lingala is primarily a lingua franca throughout the area described above. (Webbook)

7. Use in ICT / Utilisation dans les TIC

7.1 Fonts / Polices

Even though most Unicode fonts have the necessary characters, only a very few have the proper OpenType? table definitions to places accents on base glyphs? correctly, especially for the open e and the open o. Most fonts will simply misplace the acute, circumflex or caron accents ahead, behind or in case of captital, right in the character.
Même si la majorité des polices de caractères Unicode contiennent les caractères lingala, très peu les affichent correctment. La plupart ne place pas les caractères diacritiques sur le e ouvert, le o ouvert, ou les majuscules.